In a prior-art fuel-operated heater, the combustion of fuel, mostly gasoline or diesel fuel, takes place in the combustion chamber under air excess. This means that the waste gas still contains oxygen, and stoichiometrically complete combustion does not take place. The range of operation of the combustion chamber, in terms of combustion engineering, covers a lambda range (possible air-to-fuel ratios within the range of operation). To ensure the operation of the device in this range, the amount of combustion air is set during the installation of a prior-art heater or of the fan by a variable bypass opening, or the amount of fuel through the fuel feed pump is set by means of an adjusting screw. This requires a high design effort for the heater and long adjustment times.
The above-mentioned range of operation may be left during the operation of a heater for the following reasons:
Clogging of the combustion air intake or of the waste gas outlet, as a result of which the amount of combustion air is reduced, PA1 clogging of a heat exchanger connected to the heater by combustion residues, as a result of which the amount of combustion air is also reduced during the operation, PA1 change in the combustion air mass flow during the operation of the heater at different altitudes above mean sea level. PA1 case 1.1 in conjunction with 2.1, and in PA1 case 1.2 in conjunction with 2.2. PA1 1. The complicated adjustment process during the manufacture of the heater is avoided. PA1 2. A bypass is eliminated. PA1 3. The heater operates reliably during its service life even with increasing contamination of the heat exchanger. PA1 4. The range of operation (lambda range) of the combustion chamber may be narrow (low development cost), unlike in prior-art designs. PA1 5. Unlike in prior-art designs, the setting of the fuel feed pump may be inaccurate (simple manufacture).
If the operating or lambda range is left, the combustion values deteriorate. The heater no longer operates satisfactorily and it may fail.